1. Field of the Invention
This invention relates to labels including a radio frequency identification device, and more particularly to labels including a radio frequency identification device wherein the label is compatible with an in-mold process. This allows the label to be incorporated into plastic parts, such as bins and pallets, for durable tracking purposes.
2. Description of the Related Art
It is well known that items, such as plastic bins and pallets in a factory, can be tracked and identified using a radio frequency identification device (RFID). An RFID generally includes an antenna connected to an integrated circuit chip in which digital information is stored. The RFID transmits stored data by reflecting varying amounts of an electromagnetic field provided by an RFID interrogator. An RFID can now be manufactured in a very small, light weight and inexpensive unit.
A problem exists in finding a durable and cost-effective way of attaching an RFID to items to be tracked. One means for attaching an RFID to an item is an externally fastened tag. However, such tags are prone to being torn away from the item during transport. Self adhesive labels for an RFID have also been used in numerous applications where the performance and convenience of a pressure sensitive adhesive is suitable. See, for example, U.S. Pat. Nos. 6,281,795, 6,163,260 and 5,982,284. However, these labels may also be susceptible to being torn away from an item. To provide a smooth finish and excellent resistance to detachment in a molded article, embedding or in-molding of an RFID in a molded article has been proposed. See, for example, U.S. Pat. Nos. 6,302,461 and 6,206,282.
Many injection molded plastic products are manufactured from the family of polyolefins including polyethylene and polypropylene. These materials are used to produce rugged products, especially containers. The molding process includes heating a polyolefin resin to a melt-flow temperature (as high as 270° C.) and injecting under pressure into a temperature controlled mold. Depending upon mold size and complexity, this is done under pressure as high as hundreds of pounds per square inch. Typically, an in-mold label is placed in position on the wall of a mold, the mold is closed and the injection process begins. The wall temperature of the mold prevents the label from exceeding its own melt temperature. The in-mold label material is often made from an olefinic material treated for adhesion. Being similar in nature to the olefinic plastic used in the molding process, high adhesion is developed to the finished, molded article. The plastic used in the molding process is softened by heat and flows with molding pressure to fill the mold and capture the edges of the in-mold label. The surface of the mold itself retains the dimension of the finished product so the in-mold label is flush with the surface of the finished product.
A standard pressure sensitive RFID label is made using a pressure sensitive adhesive on one side of an RFID and a film or paper label stock laminated to the other, usually with another pressure sensitive adhesive. Typically, an RFID is somewhat fragile, especially in the area of the integrated chip. Inexpensive RFIDs for general label purposes are usually supplied with the antenna and chip attached to a flexible polyester film substrate. If a standard pressure sensitive RFID label is used in an in-mold process, the melt/flow temperature of typical pressure sensitive adhesives is exceeded and the label moves out of position and is distorted, delaminated or otherwise damaged a high percentage of the time. Even high performance acrylic pressure sensitive adhesives do not function well during the exposure to heat and pressure of an injection molding process. They soften excessively and lose their bond.
Thus, there exists a need for a label including a radio frequency identification device wherein (i) the label protects the radio frequency identification device chip during and after in-molding of the label in an article, (ii) the label includes a protective outer sheet that resists mechanical and chemical damage, (iii) the label provides for improved structural integrity during an in-molding process, and (iv) the label allows for improved bonding to an article during an in-molding process.